<!doctype html>
<html lang="en">
<head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">

    <title>Hello, world!</title>
</head>
<body>
<h1>Hello, world!</h1>

<div class="alert alert-primary" role="alert">
    This is a primary alert—check it out!
</div>
<div class="alert alert-secondary" role="alert">
    This is a secondary alert—check it out!
</div>
<div class="alert alert-success" role="alert">
    This is a success alert—check it out!
</div>
<div class="alert alert-danger" role="alert">
    This is a danger alert—check it out!
</div>
<div class="alert alert-warning" role="alert">
    This is a warning alert—check it out!
</div>
<div class="alert alert-info" role="alert">
    This is a info alert—check it out!
</div>
<div class="alert alert-light" role="alert">
    This is a light alert—check it out!
</div>
<div class="alert alert-dark" role="alert">
    This is a dark alert—check it out!
</div>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
</body>
</html>